What is it?

Multiple myeloma is a cancer of white blood cells, called plasma cells. Plasma cells belong to the immune system and are usually found in the lymphatic system. These cells produce proteins called antibodies, which help attack infections. In multiple myeloma, there is rapid and abnormal formation of plasma cells, which fill the bone marrow and interfere with the formation of normal blood cells. Additionally, the cancerous plasma cells produce a large amount of abnormal antibodies, which are ineffective against infections and can aggregate and damage tissues and organs (especially the kidneys). Plasma cells also tend to accumulate in the bones and cause lesions that make the bones fragile. Destruction of the bones can cause dangerous electrolyte disturbances.
Over production (proliferation) of plasma cell does not immediately cause multiple myeloma. Earlier stages include diseases called MGUS (monoclonal gammopathy of undetermined significance) and smoldering myeloma, which are a-symptomatic conditions that do not necessarily require treatment, but can precede the onset of multiple myeloma.